The present invention belongs to the field of carbon fiber composite material technology and relates to an improvement for a carbon fiber arrow shaft.
Prior arrow shafts include wooden arrow shafts, aluminum arrow shafts and carbon fiber arrow shafts. Wooden shafts have heavier masses and are not uniform thus influencing their effect on usage. Aluminum arrow shafts have lower masses but they have poor stiffness and are subject to permanent deformations. Glass fiber arrow shafts have less strength and are easily broken.
The appearance of the carbon fiber reinforced material has introduced advanced composite material into sports equipment. Such material has superior performances: lighter masses, higher strengths, and good stiffness. In making current carbon fiber arrow shafts, both carbon fibers and resins initially form a pre-impregnated material, which is then cut and twist-wound onto mandrels, and then formalized by thermosetting. Due to the overlapping joints of pre-impregnated material, surface protrusions are easily formed which affect the uniformity of arrow shafts. The non-uniform shaft wall thickness will affect the uniformity of forces applied to arrow shafts, thus resulting in bending and deformation of the shafts, and lowering the linearity of the shaft. The non-uniform shaft wall thickness will result in instability of the flight path of the arrow.
Within a certain period after shooting of the arrow, besides forward movement, the arrow shaft will have radial vibration which becomes weaker due to the damping produced by the arrow shaft stiffness and which approaches zero after a certain period of time. If the shaft wall thickness is not uniform, the stiffness along each radius direction is not symmetrical which results in an imbalance of the damping effect. The imbalanced damping will affect the motion of the arrow producing some unexpected changes in the flight path. Moreover, the arrow that is in flight will be subject to air resistance which will result in deflection from the flight path when the shaft wall thickness is non-uniform. Therefore, the non-uniform shaft wall thickness will increase the aiming errors.
U.S. Pat. No. 4,234,190 entitled "Carbon Fiber-Reinforced Plastic Arrow" has disclosed an improved carbon fiber arrow shaft (FIG. 1), which has a two-layered construction. The interior layer 12,14 utilizes a winding method, which comprises two oppositely wound carbon fiber winding layers with a winding angle between 30-45 degrees. The outer layer 16 is made by twist-winding of one to four layers of 0 degree pre-impregnated fiber material. The performance of such an arrow shaft construction are higher than those of an arrow shaft formed by complete twist-winding. However, due to the need of twist-winding one to four layers of 0 degree fiber to increase its strength, the protrusions appearing on the surface cannot be avoided. This will result in a non-uniform shaft wall thickness. Furthermore, the thickness of the carbon fibers wound on the inner layer of the arrow shaft is small such that the twist-resistance and shear-resistance are poor. When the arrow shafts are shot or aimed at the targets, the impact on hard material objects causes the two ends of the shafts to be easily cracked or broken due to greater forces imposed thereon.
One disadvantage of the manufacture technology with respect to the above-mentioned "Carbon Fiber-Reinforced Plastic Arrow" is the need for two steps in formalizing the carbon fiber tubes. The interior layer is processed on winding machines, while the outer layer is processed on twist-winding machines. Moreover, the twist-winding needs pre-impregnated materials. Thus, in the winding and twist-winding technological procedures, two fiber raw materials, namely carbon fibers and pre-impregnated materials, are needed. This results in complexity of technology, discontinuity of winding, high costs and low production efficiency.
Based on the usage features of the arrow shaft, the requirements for the stiffness at the two ends of shafts and at the central part of the shafts are different. For an ideal arrow shaft, the central part or middle section of the shaft needs a greater degree of stiffness than at the ends. Thus, when the arrow is launched, the deformation of the shaft during flight is small, the flight path is stable, and aiming precision is higher. There are large forces imposed on the arrow shaft head and tail ends during launch and impact, such that the two ends are easily cracked. Therefore, appropriate elasticity, flexibility and enough circumferential strength are needed.